An automotive battery is a rechargeable battery that supplies electrical current to a motor vehicle. Its main purpose is to feed the starter, which starts the engine. Once the engine is running, power for the car’s electrical systems is supplied by the alternator. Typically, starting discharges less than three per cent of the battery capacity. SLI (Starting, Lighting and Ignition) batteries are designed to release a high burst of current and then be quickly recharged. They are not designed for deep discharge, and a full discharge can reduce the battery’s lifespan.